Ok, I have two hard drives. One is an 8 gig that was going to hold a linux OS, the other is 40 gigs and had WinXP. Well, one day i came in and hit the power button and it just went 'click' and the led lit up and went out immediately and I couldn't do anything until I cut the power to the mobo. So I switched power supplies to a larger one, didn't help. So I asked around, people told me it was probably the North Bridge, I just replaced the mobo instead....didn't fix it (ok, i needed another mobo and cpu anyways) so I disconnected the 40 gig hard drive from the power supply and my computer started fine. Even with the IDE cable in the HDD it still starts and I am using the other hard drive now. What on earth could have caused this problem and is there any kind of fix? (Besides obviously replacing the HDD). Also, I can unplug the other HDD and take the same power connector and IDE cable and plug them into this HDD and have nothing else plugged up and it still won't power up.

I had the same problem when pressing the start button, click and nothing. But in my case it was my PS that was cooked. A PS will cook before it cooks your mobo.
I would even say that it happened twice and since I have a 3 yr. warranty the dealer put a bigger PS. So far so good.